The present invention relates to a helical scanning type magnetic recording and reproducing apparatus for recording and reproducing signals with rotary magnetic heads on and from a magnetic tape during intermittent and continuous travelling in the forward and backward directions.
Helical scanning type magnetic recording and reproducing apparatuses record and reproduce signals with rotary magnetic heads on and from a magnetic tape wound around a drum assembly having an upper drum and a lower drum. This type of apparatuses have widely been used as a video tape recorder (VTR) or a video cassette recorder (VCR).
The helical scanning type magnetic recording and reproducing apparatus is provided with a pair of rotary magnetic heads for high density recording. The rotary magnetic heads have magnetic gaps with azimuth angels set as reverse to each other.
Recording is carried out with the rotary magnetic heads so that tracks are sequentially and alternately recorded on a magnetic tape such that the tracks are inclined to the longitudinal direction of the magnetic tape. A video signal for one field period is usually recorded or reproduced for each track on or from the magnetic tape.
The helical scanning type magnetic recording and reproducing apparatus have further been used as a monitoring apparatus with a TV camera for crime prevention. Such apparatus is usually a time-lapse type magnetic recording and reproducing apparatus that picks up a video signal for one field or one frame period per specific period of time from sequential video signals output by the TV camera. The time-lapse type magnetic recording and reproducing apparatus has widely been used in banks, supermarkets and convenience stores, etc.
The time-lapse type magnetic recording and reproducing apparatus uses a magnetic tape of a specific length. For long time recording, the magnetic tape is intermittently transferred at a speed corresponding to a normal reproduction for each specific period of time for recording still pictures from the sequential video signals.
Or, a video signal for each specific period of time may be recorded on the magnetic tape while stopped among the sequential video signals for still picture recording. The magnetic tape is transferred by a specific distance and stopped for next still picture recording.
Or, a video signal for each specific period of time may be recorded on the magnetic tape travelling at a slow speed among the sequential video signals for still picture recording.
The recording methods described above complete a recording operation to one magnetic tape when recording is completed from the beginning to end of the magnetic tape. For long time recording, the magnetic tape thus must be rewound to the beginning or exchanged to another one.
Japanese laid Open patent Nos. 50(1975)-85316 and 3(1991)-194701 disclose VTRs for reciprocating recording in both the forward and reverse directions. However, the VTR disclosed in the Japanese Laid-Open patent No. 50(1975)-85316 has many rotary heads. Further, this Laid-Open patent teaches variation of angle at which a magnetic tape is wound around a drum. The Laid-Open patent thus cause a problem of incompatibility to a standard VTR.
Further, the other VTR disclosed in the Japanese Laid-Open patent No. 3(1991)-194701 conducts reciprocating recording with a drum at a rotary speed two times or more the rotary speed for normal recording or reproduction, thus causing the complexity of circuitry when the VTR is assembled as a standard VTR.
Both VTRs are capable of recording video signals of full field, however, do not provide a time lapse recording function.